1. Field of the Invention
The present invention relates to a system for providing personnel in a vehicle with information about the being of an acoustic object relative to a reference point and to a method for providing said information.
2. Prior Art
There are a large number of systems that have been developed for determining the relative positions of objects in three dimensional space. These systems utilize radio waves, electromagnetic waves, acoustic signals, and the like in different fashions to provide an operator with information about the relative positions. U.S. Pat. No. 4,734,702 to Kaplan illustrates one such system.
The Kaplan patent describes a method and apparatus for passive ranging from a moving platform to a stationary, non-cooperative emitter. The Kaplan apparatus uses a Long Baseline Interferometer to provide a very precise, but highly ambiguous, measurement of the change in phase occurring between two points along the moving platform's path and a Short Baseline Interferometer to provide a measurement of the emitter's angular position relative to the platform's path at the two points and to resolve the ambiguities in the phase change measurements of the Long Baseline Interferometer.
U.S. Pat. No. 4,797,679 to Cusdin et al. illustrates another type of system for determining the direction of incidence of electromagnetic wave signals from a distant source. The Cusdin et al. system and method measure the time of arrival of the leading edge of signals from a distant source at two relatively closed spaced receiving elements. In order to give a good degree of immunity to multipath, the times at which the instantaneous detected amplitudes of the received signals first exceed a minimal threshold value such that received signals can be satisfactorily distinguished from noise is measured in such a manner that the measured time is not affected by multipath which involves more than a few meters additional path length for the indirect, delayed signal. By making time of arrival measurements on three coplanar, non-collinear receivers, directions of incidence in three dimensions can be determined.
U.S. Pat. Nos. 4,910,526 and 5,075,694 both to Donnangelo at al. describe an airborne surveillance method and system which allows an observer aircraft to determine the position and change of position of a multiplicity of target aircraft and thus allows analysis of collision threats from these aircraft. The system uses a phase comparison direction finding antenna to determine the direction of nearby ground based SSRs and all target aircraft of interest. The system further makes use of all other available data include Mode C transponder generated altitude information of the target aircraft, the altitude of the observer aircraft, the received signal strength of both the SSR beam and the received transponder signal, the time difference of arrival between the SSR interrogation signal and the response from the target aircraft, and a variety of other factors to determine the position of the target aircraft. The system compensates for the attitude of the observer aircraft and performs optimal Kalman filtering on the input data set to produce an estimate on target position based upon prior estimates and upon information contained in the data set while making estimates of the error magnitude of each measurement and compensating for these errors. The covariance matrix Q of the Kalman filter is adaptively varied so as to optimize the estimate of the degree of correlation between various input values.
U.S. Pat. No. 5,008,679 to Effland et al relates to a method of locating an unknown radio-frequency transmitter. The method includes: (a) receipt of signals radiated from the transmitter by a plurality of receivers; (b) retransmission of the received signals to a plurality of antennas; (c) performing a time difference of arrival calculation which compensates for a relative delay value, which is a function of the distances from the transmitter to each of the receivers, the distances from each of the receivers to the antennas, and the speed of light; (d) performing a frequency difference of arrival calculation which compensates for a relative frequency value, which is a function of the relative velocity of each receiver with respect to the velocity of the Earth; (e) repeating the foregoing steps a number of times; and (f) determining the location of the unknown transmitter based on the plurality of TDOA and FDOA calculations.
U.S. Pat. No. 5,299,148 to Gardner et al. describes a process and a method for extracting or estimating directions of arrival of signals from a received data vector which has been corrupted by interfering signals and noise. The processor extracts signals by forming the scalar product of the data vector and a weight vector which is chosen such that the spectral self-coherence or conjugate spectral self-coherence of the processor output is maximized. The processor estimates the directions of arrival of signals by spectral self-coherence-selective performance surfaces for maxima.
U.S. Pat. No. 5,302,957 to Franzen describes a passive distance measuring system. The passive system operates by measuring the time interval between arrival of a precision sweep scanned signal such as a radio frequency signal at two widely dispersed different signal receptor locations on the aircraft. By knowing the angular sweep velocity of the received signals and the receptor or antenna separation distance on the aircraft, the distance of the aircraft from the scanning source of radio frequency signals may be computed with appreciable precision. The Franzen disclosure includes analog-to-digital signal conversion and modifications of the invention including optical or laser signals in lieu of the preferred microwave radio frequency signals.
U.S. Pat. No. 5,099,456 to Wells describes a passive surveillance system which provides ranging and location capability of a signal source. A single acoustic receiver in a multipath environment or, alternatively, a plurality of acoustic receivers receive the signal from the source having different propagation delays along different paths. Selection of corresponding frequency components from different paths and mixing of the correspond selected frequency components from each of the paths generates complex pseudo-noise signals that are suitable for correlation processing. Correlation processing of the mixed signals yields the time difference between the multiple paths. The maximum time difference parameters for each path are used to generate a locus line, either implicitly or explicitly. Range and location processing of the locus information identifies range and location of the signal source.
U.S. Pat. No. 5,317,323 to Kennedy et al. relates to a system for accurately locating a mobile cellular radio. The system includes plural radio receivers whose position is known, a satellite-based time source for providing the actual time of arrival of a radio signal at the plural radio receivers, and a device for removing multipath and co-channel interference from the received signals so that actual time of arrival of the radio signal may be determined accurately. The Global Positioning System may be used to provide the time signal and to provide the precise location of the plural radio receivers. The system may be used to passively determine the location of the mobile radio and may be used with a computer generated map system.
Classes of passive acoustic localization systems include those which utilize relative long towed arrays or streamers and those which utilize detached arrays or sonobuoys. The detached systems are usually deployed from low flying aircraft. The acoustic signals detected by the sensors are then transmitted to a separate computer via an RF transmitter in the sonobuoy.
To localize an acoustic source in three dimensions using sonobuoy technology requires at least two sonobuoys, each supporting a submerged sensor or vertical array. One vertical array, by itself, can only provide range and depth information. When this information is coupled with the information from a second vertical array, the source can be localized to two possible positions. To completely localize a source, a third vertical array is required.